Photosynthetic acclimation of maize to growth under elevated levels of carbon dioxide

The effects of elevated CO2 concentrations on the photochemistry, biochemistry and physiology of C-4 photosynthesis were studied in maize (Zea mays L.). Plants were grown at ambient (350 mu L L-1) or ca. 3 times ambient (1100 mu L L-1) CO2 levels under high light conditions in a greenhouse for 30 d. Relative to plants grown at ambient CO2 levels, plants grown under elevated CO2 accumulated ca. 20% more biomass and 23% more leaf area. When measured at the CO2 concentration of growth, mature leaves of high-CO2-grown plants had higher light-saturated rates of photosynthesis (ca. 15%), lower stomatal conductance (71%), higher water-use efficiency (225%) and higher dark respiration rates (100%). High-CO2-grown plants had lower carboxylation efficiencies (23%), measured under limiting CO2, and lower leaf protein contents (22%). Activities of a number of C-3 and C-4 cycle enzymes decreased on a leaf-area basis in the high-CO2-grown plants by 5-30%, with NADP-malate dehydrogenase exhibiting the greatest decrease. In contrast, activities of fructose 1,6-bisphosphatase and ADP-glucose pyrophosphorylase increased significantly under elevated CO2 condition (8% and 36%, respectively). These data show that the C-4 plant maize may benefit from elevated CO2 through acclimation in the capacities of certain photosynthetic enzymes. The increased capacity to synthesize sucrose and starch, and to utilize these endproducts of photosynthesis to produce extra energy by respiration, may contribute to the enhanced growth of maize under elevated CO2.